The present invention relates in general to insulating panels and, more particularly, to improved vacuum insulation panels having carbonized asphalt coated glass fiber fillers for use in high temperature applications and methods of making such panels.
Vacuum insulation panels are well known in the art and typically consist of a thermally insulating media which is contained within a sealed enclosure. The enclosure is evacuated to created a vacuum in the enclosure and thereby reduce heat transfer through the panel.
Conventional silica powder or glass fiber filled vacuum insulation panels are generally restricted to service temperatures below approximately 400.degree. C. Unfortunately, many applications including, for example, ovens, furnaces, and gas and diesel engine catalytic exhaust systems, require insulations which can withstand temperatures as high as approximately 1000.degree. C. These high temperature applications could also benefit from the high performance thermal insulating characteristics of vacuum insulating panels.
Above 400 DEG C., degradation of either or both the jacket member or filler material occurs over time. Most silica powder vacuum insulation panels experiences degradation of the polymer jacketing film above 90 DEG C. in applications which require a service life of several years. Even those applications which utilize high performance polymer compounds laminated with metal foils experience rapid loss of vacuum integrity above 315 DEG C. due to an increase in the jacket's permeability and outgassing properties.
Conventional silica glasses above 400 DEG C., whether in powder or fiber form, begin to deform when compressively loaded. This results in an increase, over time, in the contact area between adjacent fibers or powder particles, and, an increase in the filler material's density with a concomitant loss in the filler material's insulating performance.
While alternate filler materials, such as ceramic fibers and powders, can provide an extended temperature operating range, these materials have inherent disadvantages including high cost, poor infrared radiation blocking properties, health hazard concerns and difficulty in recycling. Carbon may be added in powder form to refractory based insulation in order to improve its radiation blocking properties. However, due to carbon's relatively high thermal conductivity, particularly in powder form at high loadings encountered for example in vacuum insulation panels, additions of carbon powder are of minimal benefit.
Accordingly, there is a need for improvements in vacuum insulation panels to adapt such panels for higher temperature applications.